1. Field of the Invention
This invention relates to an internal combustion engine of the split type operable on less than all of its cylinders when the engine is below a given value.
2. Description of the Prior Art
In general, internal combustion engines demonstrate higher efficiency and thus higher fuel economy when running under higher load conditions. In view of this fact, split type internal combustion engines have already been proposed which include active cylinders which are always active and inactive cylinders being inactive when the engine load is below a given value. Suitable means is provided for cutting off the flow of fuel (or air-fuel mixture) to the inactive cylinders so as to place the engine operation in a split engine mode where the engine operates only on the active cylinders at low load conditions. This relatively increases active cylinder loads at low load conditions, resulting in higher fuel economy.
In order to cut off the flow of fuel (or air-fuel mixture) to the inactive cylinders at low load conditions, an attempt has been made to force close the intake valves associated with the inactive cylinders regardless of crankshaft rotation. However, this requires a complex intake valve control mechanism for holding the intake valves closed during low load conditions.
With fuel injection type engines, it is conventional practice to suspend the operation of the fuel injection valves associated with the inactive cylinders during low load conditions. However, this requires fuel injection valves numbered according to the cylinders and a sophisticated fuel supply system. In addition, this system cannot be applied to carburetor type engines.